Field of the Invention
The present invention relates to electrodes comprising a plurality of connected strands and particularly anodes for microbial electrochemical cells.
Background
Electrodes comprising free strands, such as electrodes for microbial electrochemical cells comprising strands of carbon fiber bundles, have a number of limitations and shortcomings. First, these electrodes comprise individual free strands, or strands that have one end retained by a current collector and a free end that extends from the current collector. These free ends can protrude into an ion conducting membrane and cause a short in a microbial fuel cell, for example. In addition, the loose strands freely move in liquid streams and more easily dislodge bio-film and reduce the effectiveness of the cell. Furthermore, the electrical conductivity of the individual strands having a free end may be limited and the contact resistance of the strand with the current collector may be higher than desired.
Wastewater from industrial and domestic sources typically contains dissolved organics that need to be removed before the water can be reused. Traditionally, this has been accomplished by aerobic biological treatment. However, this treatment method requires aeration, which consumes large amounts of energy and thus it is an energy intensive process.
Although wastewater is typically thought of as a nuisance, it is being increasingly recognized as a resource for the production of energy, fuels, and chemicals. While anaerobic digestion has already developed into a mature technology for conversion of wastewater organics to the energetic gas methane (CH4), not all of the energy extracted from wastewater is available for use, as there are significant losses associated with the conversion of methane to easily usable energy forms such as electricity.
Recently, a new technology, referred to as Microbial Electrochemical Cells (MXCs), has gained significant attention with respect to sustainable wastewater treatment. This technology relies on specialized bacteria called anode-respiring bacteria (ARB) that oxidize wastewater organics, and transfer electrons to an anode. Microbial Electrochemical Cells can be configured as electricity-generating Microbial Fuel Cells (MFCs) or hydrogen-generating Microbial Electrolysis Cells (MECs). In a Microbial Electrolysis Cell, electrons harvested on the anode side of the reactors move through a circuit to a cathode, where water (H2O) is reduced to produce hydrogen (H2) gas by applying additional voltage between the anode/cathode bridge. The MEC is especially attractive since the produced H2 gas has higher energetic value than CH4, and can be readily converted to useful electrical power using chemical fuel cells, and is a major feedstock to the chemical and petrochemical industries. Other chemical products may be produced, such as caustic soda (NaOH), which is useful in the manufacture of pulp and paper, textiles, soaps and detergents. In electricity-producing Microbial Fuel Cells, the mode of operation is different, in that electrons from the breakdown of organic pollutants on the cathode are directly used to power a load between anode and cathode, with the additional voltage derived from the redox reaction of oxygen formation into water.